Abstract
The activated form of Ran (Ran-GTP) stimulates spindle assembly in Xenopus laevis egg extracts, presumably by releasing spindle assembly factors, such as TPX2 (target protein for Xenopus kinesin-like protein 2) and NuMA (nuclear-mitotic apparatus protein) from the inhibitory binding of importin-α and -β. We report here that Ran-GTP stimulates the interaction between TPX2 and the Xenopus Aurora A kinase, Eg2. This interaction causes TPX2 to stimulate both the phosphorylation and the kinase activity of Eg2 in a microtubule-dependent manner. We show that TPX2 and microtubules promote phosphorylation of Eg2 by preventing phosphatase I (PPI)-induced dephosphorylation. Activation of Eg2 by TPX2 and microtubules is inhibited by importin-α and -β, although this inhibition is overcome by Ran-GTP both in the egg extracts and in vitro with purified proteins. As the phosphorylation of Eg2 stimulated by the Ran-GTP–TPX2 pathway is essential for spindle assembly, we hypothesize that the Ran-GTP gradient established by the condensed chromosomes is translated into the Aurora A kinase gradient on the microtubules to regulate spindle assembly and dynamics.
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Acknowledgements
We thank S. Lizarraga for help with egg extracts, M. Inskeep for technical support, D. Golick for His-tagged RanQ69L, E. Lees for the anti-Eg2 antibody, M. Guo and the members of the Zheng lab for comments. Supported by the Howard Hughes Medical Institute (Y.Z.), by CNRS, ARC, and LNCC of France (C.P.) and by National Institutes of Health grant HD23696 (J.R.).
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Tsai, MY., Wiese, C., Cao, K. et al. A Ran signalling pathway mediated by the mitotic kinase Aurora A in spindle assembly. Nat Cell Biol 5, 242–248 (2003). https://doi.org/10.1038/ncb936
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DOI: https://doi.org/10.1038/ncb936
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